The video, filmed by a New York fund manager who was in London on business, shows Tomlinson walking alone with his hands in his pockets in front of a line of police officers, some with dogs and others equipped with riot helmets, shields and batons.

One officer appears to lunge at Tomlinson from behind, hit the backs of his legs and then push him, sending him sprawling on the ground.

Tomlinson is then shown sitting up and apparently remonstrating with the officers, as bystanders came to his aid.

Minutes later he collapsed in a nearby road.

Police attempted to resuscitate him before he was taken by ambulance to hospital where he was pronounced dead.

Answers sought

"Ian clearly had his arms in his pockets and back towards the police. There is no need for them to step in towards him," Tomlinson's son Paul King was quoted by newspapers as saying.

"[The video] clearly shows that Ian did have an altercation. Now we can say, 'yes he did.' Up until now it has been 'if'. But now we've seen it, we want answers."

Liberty, a UK-based human rights group, called for policing at public protests to be closely scrutinised.

"The images that have now been released raise obvious concerns and it is absolutely right and proper that there is a full investigation into this matter, which the Met will fully support," said Sir Paul Stephenson, the head of the Metropolitan police.